1. Field of the Invention
The present invention relates to a bearing device for a wheel, which is used in an automotive vehicle and is preloaded.
2. Description of the Prior Art
The bearing device for the wheel is rendered to be a double row rolling bearing in the form of an angular contact ball bearing or a tapered roller bearing and is applied a preload. As a method of controlling the application of a preload in the standard double row rolling bearing of a kind used in a spindle motor or a disc drive device for an information processing equipment, the method is known in which the preload control is carried out with a revolution torque. (See, for example, the Japanese Laid-open Patent Publication No. 2003-74548 published Mar. 12, 2003.)
However, since the above described preload application control method is a method, in which while a predetermined rotational torque is continuously applied to the bearing, the application of the preload is interrupted when the number of revolution of the bearing attains a target number of revolution, an equipment for the preload control tends to become bulky where it is applied to a relatively large bearing such as, for example, a bearing device for an automobile wheel. Also, in order to eliminate influences on the torque control brought about by bearing seals, the bearing seals have to be assembled after the preload has been applied, resulting in complication of the assembling work. Moreover, since there is no bearing seal during the preload being applied, there is the possibility that dusts and grits may enter in the bearing.